Nanoplasmonics offers tremendous new opportunities for fabricating ultrafast nanocircuits, as it permits miniaturization beyond the diffraction limit imposed on electromagnetic waves.
It is possible to use surface plasmons (SPs), the collective oscillations of electrons at metal-dielectric interfaces, to carry information at nanoscale. To power the circuits employing SPs, one needs an active device akin to a transistor in electronics or a laser in optics.
U.S. Pat. Nos. 7,569,188 and 8,017,406, to Bergman and Stockman, describe the principles of surface plasmon amplification by stimulated emission of radiation, and propose the use of this phenomenon to generate SPs in the active plasmonic device known as a spaser. A spaser broadly comprises a gain medium whose excitation energy is transferred nonradiatively to a coupled plasmonic resonator, increasing the amplitude of its localized SP modes. Spasers can generate much stronger coherent plasmonic fields than those created at a metallic surface excited by a laser source, due to the amplification of SPs through stimulated emission.
Experimental demonstration of the stimulated emission of SPs has resulted in the first practical realization, described in Noginov, M A et al., ‘Demonstration of a Spaser-Based Nanolaser’, Nature 2009, 460, 1110-1112, of a spaser comprising a spherical gold nanoparticle surrounded by dye-doped silica.
The operational characteristics of a spaser, such as plasmon generation rate, emission wavelength, SP quality factor, and threshold gain, strongly depend on the spaser's geometry and composition. Therefore, many spaser designs have been proposed and analyzed in search of the best performance. These include:
a gold-film plasmonic waveguide sandwiched between the optically pumped multiple quantum wells (QWs) (Flynn, R A et al., ‘Room-Temperature Semiconductor Spaser Operating Near 1.5 μm’, Opt. Express 2011, 19, 8954-8961);
a V-shaped metal nanoparticle surrounded by quantum dots (QDs) (U.S. Pat. Nos. 7,569,188 and 8,017,406);
an array of split-ring resonators on an active substrate (Zheludev, N et al., ‘Lasing Spaser’, Nat. Photonics 2008, 2, 351-354);
a bowtie-shaped metallic structure with bound QDs (Chang, S Wet al., ‘Theory For Bowtie Plasmonic Nanolasers’, Opt. Express 2008, 16, 10580-10595.; and
a metal nanogroove with QDs at its bottom (Lisyansky, A et al., ‘Channel Spaser: Coherent Excitation of One-Dimensional Plasmons from Quantum Dots Located Along a Linear Channel’, Phys. Rev. B: Condens. Matter Mater. Phys., 2011, 84, 153409.
All of these prior art designs are based on the noble-metal plasmonic nanocavities of different geometries that were coupled to semiconductor QD/QW gain media.
In this emerging area of research and development there remains a need and opportunity for new spaser designs having advantageous characteristics, including one or more of: good performance; ability to vary designs to adapt or tune spasing parameters; ease of fabrication using known methods and materials; good mechanical properties; thermal stability; chemical stability; low toxicity; and biocompatibility. The present invention addresses this ongoing need.